The control of pollution in the environment is extremely important. Environmental problems create great health risks and severely decrease the quality of life. A primary source of material for such pollution and this decrease in this quality of life is the evaporation of volatile organic compounds into the atmosphere.
Some essential features of pollution control are discussed from one aspect in U.S. Pat. No. 4,666,677 issued to Gary D. Ramus and Christopher R. Ahnen. The pollution control device defined therein is not applicable to all situations. In some cases, a more energy efficient operation is required. The structure disclosed in that patent is not applicable to a situation requiring a more energy efficient, such as a tube type, heating or cooling mechanism.
These volatile organic compounds adversely affect the ozone layer and interfere with the proper functioning of even the oxygen content of the atmosphere. The presence of these volatile organic compounds in even minute amounts can cause great harm to a person breathing the same.
Yet volatile organic compounds are very important in industry. Without these volatile organic compounds, some of the necessities of life become prohibitively expensive. Accordingly, it is highly desirable to reduce the problems caused by the use thereof and give an improved result for the conversion of these compounds into harmless materials. Typical industries, which use these volatile organic compounds in industrial processes, are the printing industry and the converting industry. The converting industry basically adapts foil, film, paper, and other packaging raw materials for use as packaging material.
It is known to use a thermal oxidizer to destroy the harmful volatile compounds from various industrial processes. Inherently the thermal oxidizer operates at very high temperatures usually in excess of 700 degrees Centigrade. Such high temperature operation creates severe problems in developing a durable device for the conversion process.
A thermal oxidizer usually is require to have at least one expansion joint and other stress relief point. This expansion joint complicates the structure of the thermal oxidizer. The stress relief point also adds complications.
In particular, the heat exchanger for use in a pollution control device generally contains a series of tubes or pipes whereby the transport gases containing the volatile organic compounds are cooled after they have been heated. For a heat exchanger, the terms, tube or pipe, may be used interchangeably. The harmless gases, thus formed by heating the volatile organic compounds to a decomposing point or destruction point, can be handled more easily and return energy to the continuing process. It is a difficult proposition to balance the structure of the tubes and support these tubes within the heat exchanger, while effecting an isolation of the two gas streams.
Within the heat exchanger, there is a cold side and a hot side, each delineated by a tube sheet. Due the greater change in temperature, there is more contraction and expansion of the tube by the hot side tube sheet. This expansion and contraction makes tube support at the hot side tube sheet a difficult proposition.
As above-indicated in the heat exchanger, there is a tube sheet support assembly, usually having a hot side sheet and cold side sheet. These sheets combine to support the tubes in the heat exchanger in a desired fashion. The integrity of the tube sheet assembly, and especially the hot side tube sheet, is highly important to the heat exchanger for use in the combustion of the volatile organic compounds. The tube sheets provide for the required separation of the two air streams. Yet while the heat exchanger is in use, the structure thereof can cause the tube sheets to crack.
Once the tube sheet cracks or otherwise becomes defective, the heat can escape to the outside shell of the heat exchanger. Contaminated air can also escape, with highly adverse environmental results. Such defects at worst destroy the unit, and at best greatly reduce the efficiencies of the unit.
This is especially critical when the Environmental Protection Agency is requiring efficiencies of combustion for these volatile organic compounds in excess of 95 percent. With the movement of the tubes caused by thermal expansion in normal operation temperature within the tube sheet, these problems are created, and a weakness in the heat exchanger and a reduction of the efficiencies thereof occur.
Other attempts to support the tube sheet are known to involve a packing system to insert insulation around the tube sheet and the tubes therein. This insulation does not withstand the strain of the process. The tubes still bind up within the hole pattern and force the sheet upward or downward during a cooling process. The hole clearance is completely lacking, and no give in the sheet is supported. This leads to a fracturing of the tube sheet and failure of the device.
It is also quite common for the volatile organic compounds or a carrier therefor to reach too high a temperature before reaching the combustion chamber. It highly desired to provide a bypass for such a device. The current bypass system is an external device on a thermal oxidizer. This external structure adds to the bulk of the device and geometrically increases the installation difficulties. Fouling of this external damper also occurs from continued condensation of airstream contaminants or pollutants, which have high boiling points.
In a known device, an external damper is used to avoid an overload on the oxidizing device or preignition of the polluted air. This external damper adds to the bulk of the oxidizing device, thereby causing a great reduction in the utility of the device. Space is sometimes a major problem for installation of a device to convert volatile organic compounds to a harmless gas.
Thus, a solution this volatile organic pollution problem must provide a device capable of operating efficiently at high temperature. There must also be a efficient provision for handling an excess of pollutants in the form of volatile organic compounds.